Almost all industries currently have at least one compressed-air network for providing compressed air to all types of machines or devices.
Many industries furthermore employ air gases provided by distribution networks, reservoirs or on-site production plants.
As a general rule, the systems for producing and providing compressed air and air gas are separate and independent, and run by different operators.
In the particular field of metallurgy, it has been proposed, in particular in documents U.S. Pat. Nos. 5,538,534 and 5,244,489, in the name of the Applicant Company, to employ a common compression group for the provision of compressed air to metal processing devices, on the one hand, and to an air-gas separation unit, on the other hand.
The object of the present invention is to provide a combined method and plant for producing and providing compressed air and at least one air gas, forming a synergy between the systems for producing and providing these fluids and making it possible to reduce investment and running costs while guaranteeing satisfactory security of the gas provision.
To this end, according to one characteristic of the invention, the process comprises the steps of generating, in nominal operating mode, at least a first and a second air flow which are assigned respectively to the provision of compressed air and the production of the air gas, and, in temporary operating mode, of assigning at least a part of the second air flow to the provision of compressed air.
According to the invention, a combined plant comprises a compressed-air provision system connected to at least a first pressurized-air source, and at least one system for producing and distributing at least one air gas which is normally connected to at least one second pressurized-air source, and means for at least temporarily switching the second pressurized-air source to the compressed-air provision system.
Thus, according to the invention, the networks for compressed air and air gas can be interconnected so as to make it possible to share the pressurized-air capacities available on site according to compressed-air demand and gas demand, making it possible to reduce the investment in pressurized air sources, typically compression units, as well as the electrical power installed and consumed, while guaranteeing increased production flexibility.
According to the invention, the priority for assigning pressurized air is given to the compressed-air provision system since compressed air is difficult to store for providing large or prolonged flow rates, whereas the air gas can be readily stored, in particular to pre-existing back-up reserves and the user systems can often make do with a reduced level of production from the air-gas production system, possibly supplemented by the reserves.
First, according to a particular characteristic of the invention, in temporary operating mode, the air gas is provided at least in part by a reservoir of the gas, typically stored in liquid form.
According to a more particular characteristic of the invention, in temporary operating mode, the second flow is assigned in full to the provision of compressed air, the switching means comprising means for isolating the gas production system from the second source which is thus assigned to the air provision.